Cryptic Species Discovered in Biological Control Agent Populations Using Molecular Data and Crossbreeding Experiments Iain D
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Two in one: cryptic species discovered in biological control agent populations using molecular data and crossbreeding experiments Iain D. Paterson1, Rosie Mangan1, Douglas A. Downie1, Julie A. Coetzee1, Martin P. Hill1, Ashley M. Burke1, Paul O. Downey1,2, Thomas J. Henry3 & Stephe G. Compton1 1Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown 6140, South Africa 2Institute for Applied Ecology, University of Canberra, Canberra, Australian Capital Territory 2601, Australia 3Systematic Entomology Laboratory, ARS, USDA, c/o National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia 20013 Keywords Abstract Biological species concept, C01, DNA- barcoding, Eccritotarsus catarinensis, There are many examples of cryptic species that have been identified through Eichhornia crassipes, Inter Simple Sequence DNA-barcoding or other genetic techniques. There are, however, very few con- Repeats, reproductive incompatibility. firmations of cryptic species being reproductively isolated. This study presents one of the few cases of cryptic species that has been confirmed to be reproduc- Correspondence tively isolated and therefore true species according to the biological species con- Iain D. Paterson, Department of Zoology and cept. The cryptic species are of special interest because they were discovered Entomology, Rhodes University, PO Box 94, within biological control agent populations. Two geographically isolated popu- Grahamstown 6140, South Africa. Tel: +27 46 603 8098; lations of Eccritotarsus catarinensis (Carvalho) [Hemiptera: Miridae], a biologi- Fax: +27 46 622 8959; cal control agent for the invasive aquatic macrophyte, water hyacinth, E-mail: [email protected] Eichhornia crassipes (Mart.) Solms [Pontederiaceae], in South Africa, were sam- pled from the native range of the species in South America. Morphological Funding Information characteristics indicated that both populations were the same species according South African Agency for Science and to the current taxonomy, but subsequent DNA analysis and breeding experi- Technology Advancement (Grant/Award Number: 84643), Working for Water (DEA: ments revealed that the two populations are reproductively isolated. Cross- NRM). breeding experiments resulted in very few hybrid offspring when individuals were forced to interbreed with individuals of the other population, and no Received: 29 January 2016; Revised: 10 June hybrid offspring were recorded when a choice of mate from either population 2016; Accepted: 10 June 2016 was offered. The data indicate that the two populations are cryptic species that are reproductively incompatible. Subtle but reliable diagnostic characteristics Ecology and Evolution 2016; 6(17): 6139– were then identified to distinguish between the two species which would have 6150 been considered intraspecific variation without the data from the genetics and doi: 10.1002/ece3.2297 interbreeding experiments. These findings suggest that all consignments of bio- logical control agents from allopatric populations should be screened for cryptic species using genetic techniques and that the importation of multiple consign- ments of the same species for biological control should be conducted with caution. Introduction are usually used to describe species (Schlick-Steiner et al. 2007; Cook et al. 2010). The result of this incongruence The biological species concept defines species as inter- between how species are defined and how new species are breeding populations that are reproductively isolated from described is that many described species may comprise other populations (Mayr 1942, 1963; Noor 2002). multiple biological species that appear to be morphologi- Although the biological species concept is generally cally indistinguishable or identical. Two or more species accepted by the majority of evolutionary biologists (Noor that have been classified as a single species due to their 2002; Coyne and Orr 2004), morphological characteristics, morphological characteristics are referred to as cryptic rather than the ability of biological entities to interbreed, species (Darlington 1940). ª 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. 6139 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Cryptic Species in Biological Control I. D. Paterson et al. There is growing evidence that cryptic species are much negative consequences of a genetic bottleneck can be more common than was previously thought (Hebert et al. overcome by combining individuals from different source 2004a; Bickford et al. 2007). The growth in the number populations (Colautti et al. 2005; Lachmuth et al. 2010) of recorded cryptic species is primarily due to the use of so it was expected that when the two populations were DNA-barcoding which can successfully distinguish allowed to interbreed, the resulting population would be between what appear to be morphologically identical spe- a more effective agent (Taylor et al. 2011). cies based on the sequence divergence within and between The Brazilian population, which was first released in species (Hebert et al. 2003). While the occurrence of South Africa in 1996, has established widely throughout many potential cryptic species have been identified using the country and contributes toward the control of water DNA-barcoding (e.g., Wilcox et al. 1997; Gomez et al. hyacinth, especially during periodic outbreaks of the agent 2002; Hebert et al. 2004a,b; Miura et al. 2005; Ward et al. that result in the collapse of water hyacinth mats at some 2008; Saitoh et al. 2015), few have been confirmed to be sites (Winston et al. 2014). Although biological control reproductively incompatible using crossbreeding experi- has successfully reduced the water hyacinth problem in ments in combination with molecular data. For some South Africa, complete control has not been achieved organisms, it is not possible to conduct crossbreeding (Coetzee et al. 2011). Cold temperatures (Coetzee et al. experiments, so multiple data sets combining morpholog- 2007a), as well as high nutrients in South African aquatic ical, ecological, and physiological data have been com- ecosystems (Coetzee et al. 2007b), are possible limiting bined with genetic data to provide a better understanding factors to the efficacy of E. catarinensis. The low genetic of whether true biological species are present (e.g., Ross diversity of the Brazilian population has been regarded as and Shoemaker 2005; Rissler and Apodaca 2007; Abad- another factor that could be limiting success, so the more Franch et al. 2013; Davis et al. 2016; Dejaco et al. In genetically diverse Peruvian population was released in press). Although these approaches are valuable, inter- 2007 with the intention of increasing the level of control breeding experiments are a more direct and conclusive provided by the agent (Taylor et al. 2011). Subsequent method of testing for reproductive incompatibility. There releases have been conducted but establishment of the are very few examples of cryptic species being verified in Peruvian population is yet to be confirmed (Winston this way. Some examples include the sweet potato white- et al. 2014). The interactions between the two popula- fly, Bemisia tabaci (Gannadius) [Hemiptera: Aleyrodidae] tions, and how each population performs at different (Xu et al. 2010; Liu et al. 2012), the dipteran vector of temperatures, is likely to play an important role in the the disease leishmaniasis, Lutzomyia longipalpis Lutz and biological control programme against water hyacinth in Neiva [Dipetra: Psychodidae] (Souza et al. 2008), and the South Africa and elsewhere in the world where E. catari- biological control agent for cereal stem borers, Cotesia nensis may be released in future (Taylor et al. 2011). sesamiae (Cameron) [Hymenoptera: Braconidae] (Kaiser A comparison of the mitochondrial cytochrome oxidase et al. 2015). This paper presents the first example of cryp- subunit 1 gene (COI) of the Peruvian and Brazilian popu- tic species confirmed as reproductively incompatible taxa lations imported to South Africa indicated a surprisingly nested within weed biological control agent populations. large sequence divergence of 5.2% between the popula- Eccritotarsus catarinensis (Carvalho) [Hemiptera: Miri- tions, suggesting the possibility that they should be con- dae] is a natural enemy of water hyacinth (Eichhornia sidered cryptic species (Taylor et al. 2011). Inter Simple crassipes (Mart.) Solms. [Pontederiaceae]) used for biolog- Sequence Repeat (ISSR) data supported this conclusion as ical control in South Africa (Coetzee et al. 2011). The 29 fixed differences were observed (Taylor et al. 2011). agent was collected in its native range of South America Sequence divergences at the COI region have been investi- from two geographically isolated populations that are sep- gated in 16 other species of Miridae and only one species arated by a distance of over 3500 km (Taylor et al. 2011). had a mean divergence value higher than 5.2%, whereas The first collection of the agent for biological control was four of the species had a maximum intraspecific diver- made in Florianopolis (Santa Catarina), Brazil in 1994, gence distance greater than this value (Park et al. 2011). and this collection was subjected to host specificity testing These data indicate that most Miridae have lower and then released throughout South